Mesothelioma diagnosis is often a case of mistaken identity. Pathologists can have a hard time telling it apart from other cancers, particularly adenocarcinoma—a type of cancer that affects the glands. One new marker—podoplanin—could help pathologists more accurately distinguish mesothelioma from other types of cancer, according to a study published online February 9 in the journal, Diagnostic Cytopathology.
Mesothelioma can be challenging to diagnose for pathologists who see just one case of this rare cancer every few years. Even with the most sensitive tests available, mesothelioma can be mistaken for other cancers, particularly adenocarcinoma. “The treatment is different. So it’s important to diagnose mesothelioma to get the right treatment,” explains Claire W. Michael, MD, Professor of Pathology and Director of Cytopathology at the University of Michigan. Mesothelioma can also be mistaken for reactive mesothelial cells—normal cells of the chest or abdominal lining that are produced in larger-than-usual amounts.
One way to diagnose meosthelioma (as well as other types of cancer) is by looking for specific antibody markers to the cancer in the patient’s blood, tissue, or fluid (effusions). Several markers are currently used to diagnose mesothelioma, including calretinin, cytokeratin 5/6 (CK5/6), and Wilm’s tumor gene product (WT-1). They all have a similar level of sensitivity.
Because no single antibody can diagnose mesothelioma with any degree of certainty, pathologists typically use a panel that includes a few different markers. The more markers the pathologist has at their disposal, the greater the chance of an accurate diagnosis. “Sometimes mesothelioma may not stain for calretinin, so to have a different antibody that will stain, if I’m still suspicious of mesothelioma, is very important,” Dr. Michael says.
Dr. Michael and her colleagues set out to test the effectiveness of podoplanin—one of the newest mesothelioma markers for fluid—to determine its sensitivity at distinguishing mesothelioma from adenocarcinoma and noncancerous mesothelial cells.
The study included samples taken from 86 patients. Eighteen of the cases were mesothelioma, 35 were reactive mesothelium, and 33 were adenocarcinomas of the breast, ovaries, and lung. Podoplanin was expressed in 94 percent of mesothelioma cases and all of the reactive mesothelial cases, but it was either weak or nonexistent in the adenocarcinoma samples.
This study provides evidence that podoplanin is effective at differentiating mesothelioma from adenocarcinoma of the lung, breast, and ovary. However, it is not able to distinguish mesothelioma from normal mesothelial cells.
No perfect marker for diagnosing mesothelioma exists, but researchers continue to develop and test new antibodies. In the future, Dr. Michael expects to see markers that further improve the accuracy of mesothelioma diagnosis. Markers may even be available to help doctors know ahead of time how mesothelioma patients will respond to treatment, as they are already able to do with markers for other types of cancer.
Hanna A, Pang Y, Bedrossian CWM, Dejmek A, Michael CW. Podoplanin is a useful marker for identifying mesothelioma in malignant effusions. Diagnostic Cytopathology. Published online February 9, 2010.